Dispersion method



Patented Aug. 10, 1937 PATENT OFFICE DISPERSION METHOD Winfield WalterHeckert, Ardentown, M, as-

. signor, by mesne assignments, to E. L du Pont de Nemours & Company,Wilmington, Deb, a corporation of Delaware No Drawing.

- 4 Claims.

- This invention relates-to theart of dispersing, and in particular, itpertains to a method of obtaining the dispersion of uniformly fineparticles of an organic pigment or pigment-like material adapted for useinartificial silk spinning solution to produce low luster yarn.

It has been found that certain comparatively low melting point,substantially colorless, organic compounds, having a plurality of nucleihighly deficient in hydrogen,-wi1l serve extremely well as pigments forvarious purposes. Although substantially larger particles thereof haveno more hiding power than a corresponding amount of many other organicor inorganic materials, when in finely divided form a product isobtained which has surprising hiding power, greater than that of some ofthe well known inorganic white pigments. Still more surprising was thefact that these pigments appear to have a greater hiding power thancould be anticipated from the average of their principalindices ofrefraction. This is probably dueto the very high birefractive propertyof the particles which is particularly brought out in their finelydivided state.

Considerable difiiculty has been experienced in obtaining organiccompounds of this character in a sufliciently finely divided form, thatis, below 2-4 microns in diameter.

Materials which melt below 100 C. have been 30 emulsified in hot waterby known methods. The

low viscosity of the medium and the excessive foam and froth produced bythe stirring generally results in wide variation in particle size. It isvery difilcult or impossible to produce emulsions 35 with practicallyall of the particles below two 45 in water.

prepared in glycerine or other nOn-aqueoushighboiling liquids.

prepared in this manner, the presence of glycerine While good emulsionscan be in the final emulsion'is' oftenobjectionable. Furthermore, manyorganic materials are slightly soluble in glycerine so that theglycerine emul- Unless great care is taken Application October 11, 19st,Serial No. 747,933

sions are not stable; the particles tend to grow into large crystals asthe emulsion cools or stands for a period of time.

Grinding methods are known whereby materials may be ground, in part atleast, to particles of small dimensions (below 2-4 microns). Thus, awater slurry maybe ground down completely in a pebble mill, ball mill,or a colloid mill, but extremely long grinding periods are required togrind all of the particles to dimensions below 2-4 microns.

Methods for particle size reduction are also known involving theapplication of large shearing forces such "as by passage of a slurrythrough a small orifice. Small particles have also been obtained bydrowning solutions of the material in water.' All-of these methods, whenapplied to certain comparatively low melting point organic substances,are open to one or more objections as referred to above. No fullysatisfactory methods exist for the removal of undesirable elements inthe dispersion such as glycerine ordeficient in hydrogen, with very fineparticle size.

Anotherobject is to eliminate excessively long grinding periods in thepreparation of concentrated dispersions and emulsions with very fineparticle size. It is one object of the invention to prepare waterdispersions and emulsions of water-insoluble, polynuclear organiccompounds, highly deficient in hydrogen, which are solid at ordinarytemperatures without the use of solvents for the compound emulsified.Another object is to'prepare emulsions or dispersions of materials whichcontain particles exceptionally uniform and very small in particle size.For example, dispersions or emulsions may be prepared, the particles ofwhich are uniformly 1-.-2 microns or less in diameter. Other objects ofthe invention will appear hereinafter.

It has been found that by properly choosing. the dispersing oremulsifying agent, dispersions of solid organic materials prepared andprocessed by any of the means common to the art may be fiocculated withsuitable reagents, filtered or otherwise concentrated and washed, andthen redispersed. During the process any undesirable elements of theoriginal dispersion medium may be eliminated and the dispersion may beconcen trated to a form suitable ior storage or shipment. It is alsopossible to form a desirable dispersion by first grinding the solidmatter forming a dis persion or emulsion, rlocculating with a suitableflocculation agent, filtering and drying.

The choice of an emulsifying agent is gov soluble in or swollen by theemulsifying medium.

dispersed with 28 cc. of triethanolemine.

Having prepared the dispersion or emulsion with the proper dispersingagent, it can be diluted and processed in some manner tocontrol particlesize, as by settling, centrifuging, selective filtration, etc. 'It isthen flocculated with an acid or other soluble electrolyte. Flocculationis most complete at the isoelectric point of the dispersing agent. Withcertain protein's it is desirable to add ammonium sulfate at this stageto aid in the precipitation of the emulsion or dispersion. Theflocculated dispersion may now be washed by any of the known methodssuch as decantation, press washing, etc. The slurry or press cake is.thenredispersed by the addition of alkali and/or additional dispersingagent followed by vigorous agitation.

EXAMPLE 1.EM'oLsmoA'rI0N 0F DIETHYLENEGLY- COIrDI-BETA-NAPHTHYL Ernest(M. P. 120) Preparation of. emulsifying agent Twenty grams of fish glueare dispersed in 600 grams of boiling water. Two hundred and eightygrams of high: pH value casein, such as that sold by the ShemeldProducts Co. of Hobart, New York, is stirred into the mixture. This isOne thousand grams of glycerine are added and the mixture is boileduntil a temperature of 128 C. is reached. At this point, the mixture isdiluted to 3000 grams with glycerlne. This will be referred to hereafteras the casein colloid.

I Preparation of emulsion Twelve hundred grams oi glycerlne are heatedto 120 C. and charged into the bowl of a small colloid mill. This millis equipped in such a manner that the material after passing between therotor and stator is returned to the bowl. Four hundred and fifty gramsof sugar are added and the material is allowed to recirculate until thetemperature reaches 120 C. At this point, 600 grams of thecasein-colloid described in the preceding paragraph are charged into themill, together with 5 grams of the product sold commercially under thename Nekal AEM and comprising an alkylated naphthalene sodium sullonateand a. protective colloid of the glue type. The temperature isallowed-to reach 120 0. at which point 'I50 grams of moltendi-ethylene-glycol-dibetanaphthyl ether are slowly added to the mill.Recirculation is continued for three to four minutes during which timethe temperature rises to about 129 C. At this point It is redispersed byadding 5% aoeaeee precipitating the acid in the filtrate and evaporatingthe excess water.

If it is desired to obtain the diethylene-glycoldi-beta-naphthyl etheras a dry organic pigment, then the-filter cake is dried in an oven at110 and disintegrated, instead of being redispersed in the mannerdescribed. The product is characterized by an unusually high hidingpower for an organic material and a very fine and exceptionally uniformparticle size. One sample had a mean diameter of 0.46 micron.

EXAMPLE 2,EMULsIFIcA'r10N or DIBENZYL Hrnno- QUINONE ETHEB. (M. P. 124)The same procedure as in Example 1 is employed, substituting dibenzylhydroqulnone ether for diethylene-glycol-di-naphthyl ether.

EXAMPLE 3.EMULSIFICATION or RETENE (M. P. 99)

42.7 grams of casein are dispersed in 400 cc. of hot water with 4.27 cc.of triethanolamine. 10.7 grams of isopropyl naphthalene sulfonate aredissolved in the solution. This is followed by 1143 grams of cane sugar.Water is added to bring up the total weight to 1600 grams.

Six hundred grams of the above solution are heated to 105 C. Two hundredgrams of molten retene are added slowly, stirring with a Hamilton-Beachdrink mixer. The temperature is maintained at about 105 and the stirringis continued until the particles average less than one micron indiameter. The emulsion is cooled and dispersed in cold water. It isflocculated with acetic acid, filtered and washed free of sugar. of itsweight of 30% sodium hydroxide and 0.5% of Nekal AEM,

and stirring with the mixer.

EXAMPLE 4.EMULs1F1oATIoN OF A CHLoRINA'rEo DIPHENYL SUoH AS AROCLOR 4465(M. P. 70-90) Seven hundred fifty grams of dispersion medium containingcasein and Nekal AEM are charged into a Dlsper-mill. It is allowed toreclrculate until the temperature reaches 105 C. The temperature ismaintained at this point by cooling with a water-jacket attached to thebowl of the mill. Two hundred fifty grams of solid chlorinated diphenylhaving a melting point from 70-90 C. (Aroclor 4465) are added. Thechlorinated diphenyl melts and is soon reduced to a particle size belowone micron in diameter. The emulsion is passed into cold water. It isfiocculated with acetic acid and ammonium sulfate, filtered and washed.It is redispersed by stirring with 5% of its weight of 30% sodiumhydroxide solution. 0.05% trichlorophenol is preferably added topreserve the casein.

EXAMPLE 5.DISPERSION or ETHYLENE GLYCOL-DI- BETA-NAPHTHYL Ernss Thismaterial melts at about 217 C. so that an emulsification process is lesssatisfactory than a grinding process for reducing the particle size.

aoeaeoe luting a previous grind before centrifuging the same. Theresulting slurry consisting of particles, approximately 60% of which arebelow 2 microns'in diameter, is diluted with water to 8% ethylene glycoldi-beta-naphthyl ether and settled or centrifuged to remove the coarseparticles. Moderate settling or 'wntrifuging will remove all particleslarger than 4-6 microns in diameter. More strenuous settling orcentrifuging will eliminate all particles above 2-3 microns. Theresulting slurry, containing only fines, is flocculated withhydrochloric acid and concentrated by filter pressing. The press cakecontaining 30-50% ethylene glycol di-beta-naphthyl ether is madealkaline with sodium hydroxide and redispersed by stirring with aLightnin mixer. If

desired, the press cake maybe stored for long periods of time, orshipped to the point at which it is to be. used and then be redispersed.Additional casein or other dispersing agents or preservatives may be'added during the redispersion step.

EXAMPLE 6.-DIsPnasIoNs or OCTACHLOBONAPHTHA- LENE Fifty pounds ofoctachloronaphthalene are ground in a Charlotte colloid mill with 50pounds of water and sufficient saponiiied shellac v to securesatisfactory dispersion. Generally, '7 35 to 8 pounds of saponifiedshellac are sufiicient.

Grinding is discontinued when the slurry contains 50 to 60% of materialbelow 4 microns in diameter. The slurry is diluted with water to 10%octachloronaphthalene and settled 20 40 inches deep in a tank for 16hours. The upper 19 inches of slurry containing most of. the fines arethen drawn off. Hydrochloric acid is added until the slurry isfiocculated. It is filtered and washed with water. The press cake ispacked in 40 drums and shipped to the point atwhich the dis-- persion isto be used. Sufdcient sodium hydroxide is added to each drum to make theslurry alkaline. Redispersion is accomplished with a Lightnin" mixer andby giving the slurry one 60 pass through a small colloid mill..

EXAMPLE 7.-D1srnasron or COMPLETELY Gnomrwran DIPHENYL Fifty pounds ofcompletely chlorinated diphenyl 55 are ground in a ball mill with lbs.of Monopole which is obtained by the process described above may beredispersed by the addition of alkali 70 and/or additional dispersingagent, followed by vigorous agitation, or the slurry or press cake maybe shipped and/or stored and then redispersed, or may be dried anddisintegrated to yield a white organic pigment of exceptional hiding 75power. If desired, the organic white pigment may be concentrated todryness, following the steps of precipitation and filtration, as bydrying in an oven, in which case the particles will be coated with 0.01%to 20%'-of the dispersing agent used in preparing the dispersion. Thepigment may be redispersed in air by disintegration or dry grinding, orin.a liquid by the application of grinding or shearing forces.

The new organic pigments can be transferred to organic vehicles withoutdrying if desired, for example, the press cake may be washed withalcohol, then incorporated in other organic solvents or vehicles.Alternatively, the pigment may be fiocculated from the aqueous phase tothe waterinsoluble, organic phase by means well known to the art, forexample, by the use of hydrophobic dispersing agents.

' White pigments owe their hiding power to the difference between theirrefractive index and that of the medium in which they are used. We havefound that a pigment must show a difference in refractive index of atleast 0.1 unit from the medium or its hiding power is very small. Muchbetter results are obtained if the difference in refractive indexamounts to 0.2, 0.3, 0.4 unit or more. Hiding power increases with thedifferfective as white pigments.

It has been found that in general the refractive index of an organiccompound increases with the number of carbocyclic or heterocyclic nucleihighly deficient in hydrogen which are present. In this specificationany complete ring of atoms is considered a nucleus. Thus, naphthaleneand carbazole contain two, and three nuclei respec tively.

Compounds containing N, S, Se, Te, have been found to have particul rlyhigh indioes and to make particularly good hite pigments. Heterocycliccompounds, highly deficient in hydrogen, containing these atoms areparticularly desirable.

Halogenation of carbocyclic and heterocyclic compounds highly deficientin hydrogen raises the refractive index still further. Of particularinterest are the completely halogenated compounds, as, for example,completely chlorinated diphenyl, naphthalene, or triphenyl benzene.

While it is preferred to use compounds for the production of thesenewwhite pigments which contain simultaneously a very high proportion ofgroups containing nitrogen, sulfur, selenium, tellurium and halogenatoms together with carbocyclic or heterocyclic nuclei highly deficientin hydrogen, it has vbeenfound that very useful white pigments can beprepared from colorless organic compoundscontaining only fourcarbocyclic or heterocyclic nuclei highly deficient in hydrogen, as forexample, from ethylene glycol di-b-naphthyl ether or N -phenylcarbazole, or

from compounds containing fewer nuclei but containing about 30%nitrogen, sulfur, selenium or tellurium, or about 60% halogen, as forexample, oxamide (31.8% nitrogen), trimethylene -trisulfone (41%sulfur), b-tetrachloronaphthalene (53% chlorine) orhexachloronaphthalene (63% chlorine).

As specific examples of additional organic compounds which may bedispersed or emulsified to particular advantage in accordance with theinvention as above set forth, the following may be named:

1. Aromatic hydrocarbons suchas triphenyl benzene, anthracene andnaphthalene-formaldehyde resins.

T accuses 2. Halogenated hydrccarhons, as herachiorobenzene,cetachiorobenzene, solid highly chlorinated diphenyls and helowanea.

3. Organic ethers and their -S,

g -Te and NH-- analogues such as ed-- benzyl hydroquinone ether,di-bennthioazylmercapto etc, and sN-dhbeta na'phthyl p-phenyleneell-amine.

4.. Organic sullones such as dine, hthyl Elli in tone or trimethylenetrisuglone.

5. Organic ketones such as di-biphenyl lsetone.

6. Organic heterocycliccompounds such as methyl dinaphtho xanthene andthianthrene.

l. Grganic tertiary amines such as triphenyl l amine.

8. Organic amidessuch as oxamide.

The present invention is not limited to the emulsiflcation or grindingprocedures described a above, or to the use of casein, Monopole oil, orsaponified shellac as dispersing or emulsifying agents. The essentialpoint is that the dispersion agent produces satisfactory dispersionsunder the conditions employed for subdivision and that these be capableof flocculation and redispersion by some convenient means. We have foundcasein or mixtures of casein with other dispersing agents such asMonopole oil, the sodium salt of isopropyl naphthalene sulfonic acid,1,1'--methylene-dinaphthyl-2,2'-disodium sulfonate or gelatin to be mostsatisfactory. Common soaps and the soaplike alkali-metal salts ofvarious sulfonic acids other than those speciflcally mentioned above,may also be used. These dispersions are easily flocculated by maklogslightly acid and are redispersed by the ad dition of a peptizing agentsuch as an alkali metal hydroxide. When casein is used as a dispersingagent a preservativeis preferably added to prevent bacterialdecomposition. Phenols are do very suitable for this purpose althoughother ma- ;terials suitable for this purpose may be used.

Phosphoric, sulfuric, hydrochloric, and acetic acids, as well as othercommon acids, may be used as fiocculating agents. Dispersions which areso protected with proteins fiocculate best at the isoelectric point ofthe protein. In thecase of casein, this is at a pH=4.6. Ammonium sulfateis also particularly eifective in flocculating proteins. lit should bepossible to prepare dispersions so with gelatin or other proteins and tofiocculate these by adjusting to the isoelectric point and addingammonium sulfate. The ammonium sulfate is washed out and redispersionagain becomes possible. Polyvalent cations fiocculateoilmany'dispersions such as those protected by the more common soaps andmay be so employed if it is desired to dry and subsequently disintegratethe concentrated dispersion. The use of polyvalent cations to flocculatethe dispersion to would be undesirable in the preferred embodimerit ofthis invention which contemplates subsequent redispersion of. theconcentrated slurry by the addition of a peptizing agent.

For the production of exceedingly fine and unior form particle sizethere is generally an optimum viscosity for the dispersion medium forevery material which is emulsified. In the past, viscosity has beenregulated by the use oi gums or other colloids such as agar-agar or gumtrage- 70 canth. The necessary viscosity is well within the skill of theart and can be easily determined from the above examples. Wateremulsions frequently foam so badly during preparation that it isimpossible to obtain uniform particle size.

to some of the material to be emed '---:.=-u

in the foam in the form at large droplets and is never emulsified, so itis frequently desirable to use a ealigned-foaming medium such as a sugarsolution in water or a glycerine-sugar SQ: lotion. Such materials arehighly undesirable in the completed emulsion, but this invention cfi'ersa means by which these materials may be used in emulsion preparation andlater be elimi nated.

This math is particularly useful for producit? ing emulsions whenconditions do not warrant the construction of expensive apparatus forthe preparation oi emulsions under pressure.

The production of uniformly finely divided dispersions is not practicalby grinding methods un- 15 less some means is provided for periodicallyremoving the fines from the coarse, unground material. If particle sizespecifications require that the separation be made in the range below8-10 I microns, this requires settling or centrifuging op- 20 erationsapplied to dilute slurries. Inasmuch as dilute slurries are not adaptedto shipment or storage for long periods of time, some means ofconcentration must be provided. The present invention ofiers aconvenient and satisfactory 25 means of concehtrating such slurries tothe point where the whole process is commercially feasible.

en materials are around in ball mills the charge is frequentlycontaminated with iron or zinc from the steel or zinc balls. The presentinvention provides a convenient means for washing out this iron or zincwith dilute acid. The organic pigments prepared according to thepractice oil this invention are particularly usefulin the delustering ofartificial silk thread. Pigments used for delustering, according tocommon practice, are introduced into the ccllulosic solution'prior toits extrusion through the spinneret. It isdesirable that the pigmentshave substantially all of their particles under 4 mi- 40 crons indiameter, and, preferably, under 2 microns; however, satisfactory hidingpower, texture and spinning (in viscose) can be obtained with a productcontaining 90% of the material as particles between 0 and 4 microns indiameter. The pigments should be uniform in size in order that they maybe easily dispersed in the cellulosic solution, e. g. viscose, whererayon of the regenerated cellulose type is to be produced, and,furthermore, in order that they may be uniformly dispersed throughoutthe artificial thread and thus give a uniform delustering effect andproduce a thread of uniform strength. Pigments consisting uniformly ofsmall particles of the size described can readily be extruded throughthe spinneret together with the cellulosic solution and do not cause anundesirable degree of abrasion on the various elements of the spinningmachine.

Any variation or modification which conforms 66 to the spirit of theinvention is intended to be included within the scope of the claims.

I claim: I

1. The method of preparing an emulsion of an insoluble, aromatic,organic, solid, colorless compound which comprises melting said compoundand emulsifying said molten compound in an aqueous medium containing adispersing agent taken from the class consisting of Turkey red oil,saponified shellac and peptized casein, cool- 70 i the emulsion tosolidify the dispersed phase, adding an electrolyte to fiocculate theemulsion, and redispersing the material by removal of the electrolyte.

- 2. method of preparing an emulsion of an insoluble, aromatic, organic,solid, colorless compound which comprises melting said compound andemulsifying said molten compound in an aqueous medium containing Turkeyred oil, cooling the emulsion to solidify the dispersed phase. adding anelectrolyte to fiocculate the emulsion, and redispersing the material byremoval oi! the electrolyte.

3. The method of preparing an emulsion of an insoluble, aromatic,organic, solid, colorless compound which comprises melting said compoundand emulsifying said molten compound in an aqueous medium containingsaponified shellac, cooling the emulsion to solidify the dispersedphase, adding an electrolyte to flocculate'the emulsion, andredispersing the material by removal of the electrolyte.

4. The method of preparing an emulsion of an insoluble, aromatic,organic, solid, colorless compound which comprises melting said compoundand emulsifying said molten compound in an aqueous medium containingpeptized casein, cooling the emulsion to solidify the dispersed phase,adding an electrolyte to flocculate the emulsion, and redispersing thematerial by removal of the electrolyte.

WINFIELD WALTER HECKERT.

